There exists a plurality of wastewater treatment processes. In an "activated sludge" process, biomass is generated and retained for a period of time in a reactor. In a typical activated sludge process, the retention time in the reactor will be approximately eight hours at design flow. The biomass concentration in the mixed liquor biomass in the reactor will be from 1500 to 3000 mg/L. The bulk of this mass will be in an "endogenous respiration state", i.e., microorganisms being in an environment with a low food to microorganism ratio, and the mass of microorganisms and the food concentration ratio remaining constant. The microorganisms must metabolize their own protoplasm. The biomass requires a large supply of oxygen. The increased oxygen demand is difficult to supply.
In an activated sludge process, as the retention time is shortened, to obtain the same bacterial synthesis, the oxygen requirement increases. This oxygen requirement is needed to grow bacterial mass when utilizing the "food", or organic waste matter, in the wastewater. Consuming more food in a shorter time requires more bacterial mass and a greater "oxygen uptake rate" (rate of oxygen consumed by the bacteria).
A "high rate" activated sludge plant carries 200 to 500 mg/L biomasses. Microorganisms are in a steady state growth phase with six hours retention time. In this state the oxygen requirement is about as high as can be practically supplied. The bacteria do not flocculate and cannot be settled-out, resulting in high effluent "BOD" (biochemical oxygen demand) as well as high solids that will not meet typical 30 mg/L BOD and 30 mg/L solids effluent requirements. Typically, the effluent would be approximately 100 mg/L BOD and 100 mg/L solids. BOD is a measurement of biologically degradable organics in wastewater.
In a "dispersed" activated sludge process, the treatment plant loading maintains the bacteria in the "log growth phase" i.e., a bacterial growth phase characterized as having a maximum rate of synthesis. At the end of the log growth phase the microorganisms are growing at their maximum rate. There is little flocculation so that the mixed liquor is a discrete bacterium. A very small active mass can consume the food. All of the food is used in creating mass, so there is no oxygen requirement for endogenous respiration. Less oxygen is required. The bacteria in such a dispersed phase more quickly and completely consume the food. With food supply varying, some flocculation can occur at low flow rates.
The maximum oxygen transfer rate and the maximum rate of growth of bacterial mass during high load conditions are process limitations. Also, lower wastewater loads can result in flocculation and higher BOD and solids in the effluent, as well as higher oxygen requirements. A reduction of the effluent BOD and solids below approximately 60% of the influent BOD and solids has not been achieved.
The various types of activated sludge systems can produce quality effluent in some cases but all result in large quantities of sludge for disposal. Also, in high rate activated sludge processes at 120 pounds of BOD/1000 ft.sup.3 per day or above, it becomes difficult to transmit enough oxygen to the water to maintain satisfactory dissolved oxygen levels.
In waste treatment processes, to maintain the log growth phase, the organic concentration in the liquid surrounding the microorganisms must be high. It is difficult to produce a stable effluent while the microorganisms are in log growth phase because a large concentration of food will typically pass through the plant unconsumed by the bacteria, during the growth of the bacteria. In waste bacteria aerobic processes a maximum rate of oxygen is demanded. The maximum oxygen transfer rates from available diffused-air equipment limits the rate of growth in the log growth phase.
A "submerged media" process has microbes attached to the media. The liquid-containing waste is aerated and circulated through the media. Instead of having flocculated clumps of endogenous bacteria circulating in the mixed liquor, the inactive growth is attached to the media with active bacteria on the surface. There is an aerobic endogenous layer below the active bacteria layer, and then an anaerobic layer from there to the media. Being attached, succeeding layers build up over existing layers. The process produces about the same mass of solids as complete mix-activated sludge, but may be retained longer and be reduced in volume by longer endogenous respiration or anaerobic digestion. Process loading is limited by maximum aeration and maximum mixing. As the solids build up they have about the same weight as the liquid. This allows large accumulations that may start sloughing-off from circulation currents. The accumulations may plug up the media.
The bacterial growth is fastest where the influent enters the process and the microbes have access to nearly unlimited food. As the microbes are attached they never move from the food source as they would in suspended growth aeration systems. Solids must be removed at frequent periods. Food-to-organism distribution is uneven depending upon distance or position related to the food source.
The process cannot be operated at a high rate because of difficulty of dispersing oxygen and food through the media. The process produces sludge which must be wasted in some manner. The effluent is low in solids and BOD because of the microbes being attached to the media, but only if the media is purged of solids often enough to prevent sloughing.
In a "ring lace" process, the media surface is shaped like long stretched coil springs. The media coils are composed of a synthetic material. The coils are not closely spaced making it easier to circulate liquid and oxygen therebetween. The process cannot be considered a high rate system because of the small amount of available surface area. The process does not work as well in colder climates due to the fact that less heat is generated due to the small surface area of the media. Some sludge is produced. Part of the food is utilized by suspended microbes and part of the food is utilized by attached microbes. No clarifier is required because the attached microbes consume enough of the dispersed microbes to keep effluent quality satisfactory. Solids must be shaken from the ring lace frequently to avoid sloughing and effluent deterioration.
In a "trickling filter" process, liquid-containing food flows in a thin film over media coated with both a fixed film of microbes and a fixed film of liquid over the microbes. To be efficient, the hydraulic loading must wash the attached growth from the media to keep the surface active. A clarifier must remove the sloughed solids. High rate trickling filters stabilize the removal of organic matter to only about 75%. For stronger wastes, recirculation is required to help dilute the incoming load and carry the untreated load back for further treatment. These filters have been loaded up to 90 lb/1000 ft.sup.3 /day.
Trickling filters known as "super rate" trickling filters have been loaded as high as 100 lb/1000 ft.sup.3 /day. These filters are vertical filters with great depth having media with attached microbial growth. The filters produce a large volume of solids that must be wasted. The filters carry microbial growth in recirculation liquid. The attached microbial growth only treats a small portion of the liquid because the oxygen and food can't be transferred fast enough to the attached microbial growth.
In existing trickling filters, the effluent BOD-and-solids load is directed to the media. Bacteria and protozoa are attached to the media. This is not conducive to effective treatment because neither bacteria nor protozoa is in the most advantageous place to be optimally effective. This process has used two stages. The resulting effluent is about 50 mg/L BOD and 50 mg/L solids. Waste solids are created which require disposal.
Aerobic treatment processes generate large volumes of solids. The shorter the retention time and the higher the loading, the greater the amount of solids produced. The treatment processes are designed to retain the solids to be used in the settling process which is necessary for acceptable effluent. This excess volume of solids must be disposed of by means that are becoming less and less ecologically sound. A disposal of the solids can result in high costs and may be banned altogether. In high rate aerobic processes, it has been difficult to transfer enough oxygen to support the biological mass. This has limited the BOD-and-solids loading and/or increased the process cycle length.
The present invention recognizes that it would be desirable to provide a process that works with just active mass. The present invention recognizes that it would be desirable to treat with the minimum number of bacteria. The present invention recognizes that it would be desirable to provide a process designed to work with large mass bacteria. The present invention recognizes that it would be desirable to provide a process to work with a minimum number of protozoa. The present invention recognizes that it would be desirable to provide a process having the media surface area covered with a minimum number of protozoa.